The present invention relates to automatic replenisher systems for processors of photosensitive material. In particular, the present invention relates to an improved control system for controlling a replenisher which provides replenisher fluid to a processor.
Photographic processors require replenishment of the processing fluids to compensate for the lowered chemical activity of the fluid which results from processing of the photosensitive film or paper. Replenishment systems originally were manually operated. The operator would visually inspect the film being processed and would manually operate the replenisher systems as he deemed necessary. The accuracy of manual replenisher systems is obviously dependent upon the skill and experience of the operator.
In recent years, automatic replenishment systems have found increasing use. These systems typically utilize film density measurements and, in some cases, film speed measurements to control the operation of the replenishment system. Examples of previous automatic replenishment systems are shown in a patent application by Gaskell and Charnley, Ser. No. 590,078, now U.S. Pat. No. 4,057,818 filed June 25, 1975 and assigned to the same assignee as the present application, and in U.S. Pat. Nos. 3,529,529 by Shumacher, 3,559,555 by Street, 3,561,344 by Frutiger et al, 3,696,728 by Hope, 3,752,052 by Hope et al, 3,822,723 by Crowell et al, and 3,927,417 by Kinoshita et al.
The prior art automatic replenisher systems may be characterized generally as analog electrical or electromechanical systems. As a result, they are generally difficult to calibrate, are subject to drift, and are relatively complex electrically or mechanically. There is a continuing need for simpler, more reliable automatic replenishment systems.